Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$93.49	6.802%	$99.8492	$99.85	$99.85	$99.80
Purchase #2	$36.92	3.660%	$38.2713	$38.27	$38.25	$38.30
Purchase #3	$41.54	7.783%	$44.7731	$44.77	$44.75	$44.80
Purchase #4	$8.41	12.708%	$9.4787	$9.48	$9.50	$9.50
Purchase #5	$69.75	3.568%	$72.2387	$72.24	$72.25	$72.20
Purchase #6	$187.30	4.362%	$195.47	$195.47	$195.45	$195.50
Purchase #7	$233.46	7.318%	$250.5446	$250.54	$250.55	$250.50
7 purchase totals =	$670.87		$710.6256	$710.62	$710.60	$710.60